1. Field of the Invention
The present invention relates to a stator for an automotive alternator and particularly to a construction of a stator core formed by laminating a press-formed magnetic steel sheet.
2. Description of the Related Art
FIG. 20 is a plan explaining a process for forming a laminated body by a first sheet in a conventional stator for an automotive alternator described in Japanese Patent Non-Examined Laid-Open No. 2001-112197, for example, FIG. 21 is a cross section taken along line XXI—XXI in FIG. 20 viewed from the direction of the arrows, FIG. 22 is a plan showing a second sheet in the conventional stator for an automotive alternator, FIG. 23 is a cross section taken along line XXIII—XXIII in FIG. 22 viewed from the direction of the arrows, FIG. 24 is an exploded perspective showing a process for inserting conductor segments into a stator core in the conventional stator for an automotive alternator, and FIG. 25 is a partial cross section explaining a mounted state of a stator winding in the conventional stator for an automotive alternator.
A conventional stator 1 is constituted by: a cylindrical stator core 2 in which slots 3 are formed at a predetermined pitch in a circumferential direction so as to open onto an inner circumferential side; a stator winding 4 installed in the slots 3 of the stator core 2; and insulators 5 mounted inside each of the slots 3.
The stator core 2 is provided with: a laminated body 7 constituted by a first sheet 6; and second sheets 8 disposed at first and second axial ends of the laminated body 7.
As shown in FIG. 20, the laminated body 7 is formed into a cylindrical shape by winding up the first sheet 6 for a predetermined number of winds into a helical shape, the first sheet 6 being formed by using a press die to punch recess portions 6a at a predetermined pitch in a strip-shaped sheet composed of a magnetic material. Here, the recess portions 6a are superposed in an axial direction of the laminated body 7, constituting first slot portions 3a. In the laminated body 7, the first sheet 6 is laminated with the press punch direction aligned, as shown in FIG. 21, and burrs 6b extending in the press punch direction remain on each layer of the first sheet 6 on inner wall surfaces of the first slot portions 3a. 
As shown in FIG. 22, the second sheets 8 are each formed into an annular shape by using a press die to punch a flat sheet composed of a magnetic material having a sheet thickness greater than the first sheet 6. Here, second slot portions 3b corresponding in position to the first slot portions 3a are simultaneously press-formed. As shown in FIG. 23, eased portions 8a are formed on a first end side of the second sheets 8 at edge portions of the second slot portions 3b. Moreover, the second sheets 8 are formed so as to be equal in diameter to the laminated body 7.
The second sheets 8 are disposed at first and second end surfaces of the laminated body 7 such that the positions of the first slot portions 3a and the second slot portions 3b align and the eased portions 8a face away from the laminated body 7, and the stator core 2 is prepared by performing several strips of laser welding so as to extend in an axial direction from a first end portion to a second end portion on the outer circumferential surfaces thereof. Moreover, the first and second slot portions 3a and 3b align in an axial direction, constituting the slots 3.
As shown in FIGS. 24 and 25, the stator winding 4 is constructed using a plurality of conductor segments 9 by joining together end portions of the conductor segments 9 by a joining method such as welding, etc. The conductor segments 9 are each prepared by bending into a U shape a short length of copper wire having an electrically-insulating coating. Here, large and small first and second conductor segments 9a and 9b form a basic unit and a plurality of these units are used. The conductor segments 9 are housed in the slots 3 so as to be surrounded by the insulators 5 such that the insulators 5 are installed between the conductor segments 9 and inner wall surfaces of the slots 3. Together with the electrically-insulating coating covering the copper wire of the conductor segments 9, these insulators 5 ensure electrical insulation between the conductor segments 9 and the stator core 2.
The conductor segments 9 and the insulators 5 are inserted into the slots 3 of the stator core 2 in a direction aligned with the press punch direction of the first sheet 6, in other words, from top to bottom in FIG. 25. The stator winding 4 is prepared by bending first end portions of the conductor segments 9 extending outward from the slots 3 of the stator core 2 as indicated by the arrow in FIG. 25 and joining the first end portions to second end portions of conductor segments 9 separated by a predetermined pitch.
In the conventional stator 1 constructed in this manner, the opening edge portions of the slots 3 at the first and second axial end surfaces of the stator core 2 are constituted by the eased portions 8a of the second sheets 8, and the burrs 6b formed by press punching are present only inside the slots 3. Thus, damage to the electrically-insulating coating of the conductor segments 9 caused by the burrs 6b is avoided during insertion of the conductor segments 9, during bending or joining of the end portions of the conductor segments 9, and during shaping of coil ends of the stator winding 4 after joining of the conductor segments 9, thereby improving electrical insulation.
In the conventional stator for an automotive alternator, because the stator core 2 is prepared, as described above, by preparing the laminated body 7 by winding the strip-shaped first sheet 6 in which the recess portions 6a (the first slot portions 3a) are formed by press punching into a helical shape for a predetermined number of winds, disposing the thick annular second sheets 8 in which the second slot portions 3b are formed by press punching at first and second ends of the laminated body 7, and integrating the laminated body 7 and the second sheets 8 by welding, the following problems arise, preventing cost reductions:
First, because the first sheet 6 and the second sheets 8 used have different sheet thicknesses and punched shapes, two types of magnetic material and two types of press die are required, increasing the number of materials, manufacturing processes, and types of equipment; and
Second, because the second sheets 8 are disposed on both the first and second ends of the laminated body 7, two second sheets 8 are required, increasing the number of materials and manufacturing processes.